Accuracy of phase shift measurement

[Soh82]

Dear all,

I am trying to choose a SCOPE for performing phase shift measurements between 2 AC signals.

I would like to be able to measure the phase in order of 0.5° (or ~ 23 microseconds difference).

I would like to ask you some advise to choose my device:

- Should i check only the sampling rate of the scope for that ?

- Should i check the bandwidth of the scope?

- can i perform this measurement with LabVIEW ?

Many thanks in advance

[cheggers]

Hi Soh82,

Yes, for accurate phase shift measurement both sampling rate and bandwidth are important.

1. Sampling Rate: To measure a phase difference of approximately 0.5° or ~23 microseconds, you need a sampling rate that is high enough to capture the signal's details accurately. This ensures capturing enough samples per cycle for accurate phase calculations (referencing the Nyquist criterion). Generally, a sampling rate at least 10 times higher than the highest frequency component of your signal is recommended. For example, if your signals are up to 1 MHz, a sampling rate of at least 10 MHz would be advisable.
2. Bandwidth: The bandwidth should be sufficient to capture the highest frequency components of your signals without significant attenuation. The bandwidth should typically be at least 3 to 5 times the highest frequency you intend to measure. If you are working with signals up to 1 MHz, a scope with at least 5 MHz bandwidth would be appropriate.
3. Using LabVIEW for Measurements: Yes, LabVIEW can be used for phase shift measurement. It offers built-in functions for acquiring data from oscilloscopes and performing phase calculations on the captured waveforms (in the signal processing functions palette, there should also be some existing examples how to use this function). The accuracy of the measurements will still depend on the specifications of the hardware (such as sampling rate and bandwidth) used to capture the signals.

Thanks!

[Henrik_Volkers]

If 0.5° phase results in about 23E-6 s delay, the frequency is about 60 Hz.

I would use my soundcard ...

a scope with >= 10kSPS should do it.

But that depends on your signals and how fast the phase is changing, noise, ...

Another important point are the complex impedances of your sources, the scope and the cables.  

Assuming both scope inputs use the same range and input impedance, you should check the result with swapped channels in the frequency range of interest, to proof the interchannel delay.

For 0.5° at 60Hz and a sine shape , capture 30 periods (500ms signal) run tone detection (extract single tone information) on both signals and calc the phase difference. Should easily fit your needs.

For more sophisticated results post some data, by copy the diagram with data into a new vi, make current values default, save and post the vi.